Limit of Laser Protection Capability of Arcsine Coded Imaging System
Objective Traditional imaging systems,due to their focal plane structure,exhibit significant optical gain but have a limited depth of focus.This creates a paradoxical scenario:achieving high image quality comes at the expense of weak laser protection capabilities.Established methods for laser protection in optoelectronic imaging systems encounter challenges including reliance on prior knowledge,bandwidth limitations,and degraded image quality.To address the conflict between image quality and laser protection,researchers utilize wavefront coding technology,leveraging its deep focus characteristics and light field regulation.This enables defocusing the image plane to enhance the system's laser protection capacity without compromising image quality.While wavefront coding can achieve a balance,previous studies have placed excessive focus on how defocus affects laser protection,overlooking its consequential impact on image quality and essentially ignoring how image quality can restrict laser protection.Therefore,investigating the balance between laser protection capability and image quality in wavefront coded imaging systems,as well as understanding the limits of the system's laser protection,is of utmost importance.We aim to examine this balance within the context of the arcsine wavefront coded imaging system and discern the limits of its laser protection capabilities.Methods Using the arcsine phase mask(ASPM)as an exemplar,we build imaging and laser transmission models for a defocused wavefront coding system.The trends are investigated in image quality and laser protection as the defocus parameters shift.By employing a decoupling approach,we take the system's image quality as a fundamental constraint.To ascertain the system's maximum permissible defocus parameters,we introduce quantitative evaluation metrics.Furthermore,our study assesses the system's laser protection capability based on these parameters,providing insights into the protection limits of wavefront coded imaging system.Results and Discussions Numerical simulations of the imaging model demonstrate that in conventional imaging system,increasing defocus parameters gradually blur the resulting image,leading to a significant deterioration in image quality.In the case of the ASPM wavefront coded imaging system,the coded image,modulated by the ASPM,also becomes blurred.However,by selecting an exploratory parameter K=4.25×10-4,the decoded image closely resembles the imaging effect of the conventional imaging system in its non-defocused state.This indicates that the ASPM wavefront coded imaging system achieves superior depth-of-focus extensions through joint hardware and software optimization(Fig.5).To quantitatively evaluate the changes in image quality with defocus parameters,we employ peak signal-to-noise ratio and structural similarity metrics.Based on the Rayleigh criterion and using the peak signal-to-noise ratio and structural similarity values of the conventional imaging system as a threshold,we compute the defocus limit for the wavefront coded imaging system to be 9.70A.The numerical simulation results of the laser propagation model reveal that as defocus parameters increase,the size of the light spot at the imaging plane of the conventional system grows rapidly.This leads to a sharp decline in light intensity and a significant reduction in the maximum single-pixel receiving power.However,the wavefront coded imaging system,with its defocus invariance,exhibits a more gradual decline in its maximum single-pixel receiving power(Fig.6).Furthermore,both the conventional and wavefront coded systems show a decreasing trend in echo-detection receiving power(Fig.7 and Fig.8).At the same defocus parameters,the echo spot size of the wavefront coded imaging system is similar to that of the conventional imaging system,and their echo-detection receiving power are essentially the same.Therefore,the defocus limit of the imaging system determines the boundary of its laser protection capability.Conclusions By considering the image quality of the ASPM wavefront coded imaging system as a fundamental constraint,we establish that the maximum permissible defocus parameter for the wavefront coded imaging system is determined to be 9.70A.When compared to the non-defocused state of the conventional imaging system,at this specific defocus parameter,the ASPM wavefront coded imaging system experiences a significant decline in the maximum single-pixel receiving power,reaching 96.37％.Additionally,the echo-detection receiving power drops to 0.217％o.These findings highlight the enhanced capabilities of the wavefront coded imaging system,with an improvement over one order of magnitude in anti-laser damage and three orders of magnitude in anti-laser active detection.
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